File folders refer to the variety of stationeries used to hold or store files, so it is simply impossible to make a list of all the widely differing file folders available now in the market. The file folders mentioned here are of special expandable types, and the most conventional structure of these types is shown in FIG. 1. The file folder consists of the front side 11, the back side 12, the two lateral sides 13, one flap 14 and several dividing sheets 15. Consequently, the divided spaces 16 are formed by the sheets. Because of its continuous W-shaped cross-section design in its two lateral sides, it is capable of flex-like snake-belly extension and renders the divided spaces 16 formed by dividing sheets 15 changeable in accordance with the flex of the two lateral sides 13. Thus, the file folder 10 will change its shape and appearance as the amount of file content varies. The conventional expandable file folder will keep its good orderly shape if A4-sized files are placed inside the file folder 10, because the width of this type of file paper is almost the same as that of the divided spaces 16 and can expand the folder in an evenly manner. However, if inside the folder are put files or stationeries (small notebooks, pencil boxes, pens and the like) of much smaller sizes than the divided spaces but with a considerable thickness, the two lateral sides will be expanded unevenly and the folder will look very ugly.
Therefore, another kind of expandable file folder has been produced. As shown in FIG. 2, it differs from the conventional type in that an inflexible case 23 is inserted between the front and back sidewalls 21 22 of the file folder 20. The divided spaces near the front and back sidewalls 21 22 are expandable. The fixed space provided by the case 23 can be used to accommodate the files and stationeries other than A4-sized files, such as small notebooks, pencil boxes and pens. The problem of crushing will also be solved. However, the following problems still exist for this kind of file folder structure.
As shown in FIG. 3, the case of the above-described expandable file folder 20 is inserted between the front and back sidewalls 21 22 of the file folder 20. As the case is usually only 2˜3 centimeters thick, it is very difficult for the case alone to support the whole file folder and make it stand steadily. Although the bottom area of the file folder 20 will be increased in accordance with the amount of files placed inside the front or back expandable sections 24, the increased area is always indefinite. Therefore, when the user places the folder on the desk or on the floor, it will tend to fall down for loss of balance. Moreover, when the folder falls down, the surfaces of the front and back sides will get dirty, and the user will have to spend more time cleaning the folder. In addition, if the user wants to look for, take out or put in a file stored in the expandable sections, he has to stick open the storing space with one hand and look for, take out or put in a file with the other hand. This is because the expandable sections 24 are capable of restoration; once let go of, it will be restored to its original flat and shrunk condition and make the above actions difficult. This is where its inconveniences lie for the user.
Thus, to overcome the aforementioned problems of the prior art, it would be advancement in the art to provide an improved structure that can significantly improve the efficacy.
To this end, the inventor has provided the present invention of practicability after deliberate design and evaluation based on years of experience in the production, development and design of related products.